Nitrate oxide heap leaching method

Abstract

A method of extracting copper from a sulfide mineral ore, the method comprising the steps of stacking the ore to form a heap, in a leaching step, irrigating the heap with a first irrigation solution containing an acidic nitrate solution and a nitrite, thereby causing oxidation of the sulfide minerals within the heap, nitric oxide gas released during the oxidation of sulfide minerals within the stack is oxidized by oxygen to form nitrogen dioxide, and the nitrogen dioxide is hydrolyzed to form nitric acid and / or nitrous acid in the first irrigation solution within the stack to continue the leaching step and reduce the loss of nitric oxide from the stack.

Description

Background of the Invention

[0002] The present invention relates generally to a method for leaching base metals from ore heaps. The invention is particularly suitable for treating primary copper ores containing chalcopyrite and secondary sulfide minerals such as chalcopyrite, bornite, chalcocite and covellite in an oxidizing environment.

[0003] The oxidation of nitrates and nitrites in aqueous solutions of sulfuric acid is extensively described in the literature and patent prior art.

[0004] Anderson (2003) stated that the addition or presence of NO2 - Instead of NO3 - Enhanced reaction rate of chalcopyrite oxidation. Results presented by Gok and Anderson (2013) demonstrated that effective leaching of chalcopyrite was achieved by leaching finely ground mineral (d80 15 microns) with 0.1M NaNO2, 1M H2SO4 at temperatures exceeding 100°C (110-120°C). The use of sodium nitrite was found to be more effective than sodium nitrate under these extreme conditions.

[0005] et al. (2009) described the kinetics of chalcopyrite leaching in sulfuric acid solution using sodium nitrate as the oxidant. The results showed the importance of temperature and the requirement for fine grinding to achieve satisfactory copper dissolution. It was found that copper dissolution increased with increasing sulfuric acid and sodium nitrate concentrations and decreasing particle size.

[0006] Baldwin and Van Weert (1996) compared the rate of oxidation of ferrous iron to ferric iron in the presence and absence of nitrate or nitrite. The rate of Fe(II) oxidation was increased by the addition of nitric acid and nitrate, and significantly increased by the addition of nitrite. Thus, the use of nitrite-assisted oxidation in autoclaves used in mineral processing may result in more efficient operation.

[0007] Ricardo Andres Soto Mellado ( & Mellado, 2018) describe methods for oxidation of copper sulfide minerals and leaching in acid chloride and sulfuric acid chloride / nitrate solutions. The publication discloses the treatment of low-grade copper sulfide ores in an acidic chloride-nitrate medium. The concept of pre-treating the ore in an agglomeration step and a subsequent slaking step is disclosed. The mechanism of chalcopyrite leaching in acidic ferric sulfate and sulfuric acid with chloride solutions is disclosed, as well as the effect of adding nitrates (as sodium nitrate or ferric nitrate) to increase the oxidation potential of the solution. On a specific low-grade ore (0.12% Cu), 27% metal dissolution was achieved on a ground sample with a 25% solids content. &Mellado concluded that despite improving mineral degradation, the addition of sodium nitrate and ferric nitrate in combination with sodium chloride and sulfuric acid during the pretreatment of copper sulfide minerals did not significantly affect the final copper dissolution.

[0008] US 9683277 discloses nitrate-assisted leaching using ferric nitrate. The role of ferric nitrate and the method of generating the reagent are disclosed.

[0009] WO 2012 / 162851, WO 2017 / 063099, US 9683277 and CL 43295 each disclose a heap leaching process in which iron nitrate, ammonium nitrate or sodium nitrate acts as an oxidant in sulfuric acid or an aqueous sulfuric acid / chloride solution.

[0010] US 5096486 describes a sulfuric acid leaching process which uses sodium nitrite to treat sulfide materials (including copper sulfide) by leaching under relatively mild oxygen pressure and temperature conditions.

[0011] US 3888748 describes a leaching process using nitric acid and sulfuric acid at a temperature of at least 50°C, demonstrating the oxidative advantages of adding nitric acid (or nitrates) to sulfuric acid leaching.

[0012] US 4,647,307 discloses a method for hydrometallurgical recovery of precious metals from an ore or concentrate containing at least some arsenopyrite or pyrite. The method includes forming a gas phase and a liquid slurry containing an ore or concentrate as a solid phase and water as a liquid phase of the slurry in a common volume space, in which an oxidation-reduction reaction between arsenopyrite or pyrite and oxidized nitrogen species is achieved, wherein the nitrogen has a valence of at least +3, thereby dissolving arsenic, iron and sulfur in arsenopyrite or iron and sulfur in pyrite in the liquid phase, and producing nitrogen monoxide in which nitrogen has a valence of +2 in the liquid phase; releasing at least a portion of the nitrogen monoxide from the liquid phase into the gas phase, oxidizing the nitrogen monoxide in the gas phase to form nitrogen oxide species in which nitrogen has a valence of at least +3; and absorbing the nitrogen oxide species into the slurry, wherein the nitrogen oxide species become available for the oxidation-reduction reaction. The resulting treated slurry is subjected to solid-liquid separation to produce a solid residue and a liquid portion. The precious metals are recovered from the solid residue. The liquid portion is recycled in the process.

[0013] The process disclosed in US 4,647,307 requires operation at an oxygen partial pressure above the ambient oxygen partial pressure in air.The process describes the use of a pressurized vessel (autoclave) to process ground concentrate or ore in a slurry at a temperature of 60°C to 180°C.

[0014] WO 2021 / 186376A1 describes an oxidative bioleaching method for leaching base metals from an ore, the method comprising an ore agglomeration step, an ore stacking step in which the agglomerated ore is stacked to form a heap, a maturation step, a rinsing step, an inoculation step and a leaching step, and wherein, during the ore agglomeration step, the ore is contacted with an acid solution containing nitrates and nitrites, thereby accelerating the leaching rate in the leaching step. Another object of the present invention is to provide a bioheap leaching method using nitrogen compounds as oxidants, wherein the inoculation and bioleaching steps are not adversely affected due to the inhibitory effect of nitrate compounds on microbial growth. The method is limited by the need to include ore agglomeration and maturation steps.

[0015] Although effective to a limited extent, bioleaching processes generally have slow reaction rates and slow initial heat generation. As a result, bioleaching processes are ineffective for the treatment of ROM ores.

[0016] Prior art methods have shown that nitrates in acidic media offer an option for leaching sulfide minerals at acceptable kinetic rates. However, these applications involve high temperatures and pressure levels. In addition, prior art methods have shown that agglomeration and maturation steps are necessary to create reactive conditions in a heap leaching environment, thereby achieving relatively high acid and nitrate conditions in an almost closed system, resulting in active oxidizing conditions.

[0017] In nitrate leaching operations, NO x (NO and NO2) gases leave the system during the leaching cycle and ore agglomeration step and contribute to high nitrate and acid consumption rates in the heap leaching stage. To the applicant's knowledge, capturing NO has only been achieved commercially in a closed system, under elevated pressure conditions, or by using a gas capture and scrubbing step in the ore agglomeration stage prior to heap construction (as part of the ore agglomerator design). x Direct nitrate leaching of gases.

[0018] NO leaving the surface of the heap during the leaching cycle x The gases - mainly NO (low solubility in aqueous solution) - are difficult to capture and the overall nitrate consumption remains high, in the range of 10-20 kg / T or above 20 kg / T. In a heap leaching process operating at ambient pressure, efficient recycling of NO and NO2 gases has not been demonstrated.

[0019] Heap leaching processes for unagglomerated ore or ROM ores where heat generation by pyrite oxidation is essential for copper recovery have not been described.Comminution and agglomeration of low grade ores significantly increases capital and operating costs.

[0020] The present invention aims at at least partially to solve the above problems. SUMMARY OF THE INVENTION

[0022] "Heap" as used herein includes ore processed in irrigated piles, in columns, in vats or in an oredump.

[0023] All solution potential values ​​described herein are in mV relative to the standard hydrogen electrode (SHE).

[0024] The present invention provides a method for extracting copper from a sulfide ore, wherein the sulfide ore is selected from ROM ore, crushed ore or crushed ore subjected to acid agglomeration, and the method comprises the following steps:

[0025] a) piling up ore to form a heap;

[0026] b) In the leaching step, a nitrate-containing solution (NO3 - ) solution and 50–500 ppm nitrite (NO2 - ) to irrigate the heap, thereby causing oxidation of sulfide minerals within the heap;

[0027] c) adding air or oxygen or oxygen-enriched air to the stack;

[0028] d) oxidizing NO gas released during oxidation of sulfide minerals in the heap by oxygen to form nitrogen dioxide (NO2); and

[0029] e) hydrolyzing nitrogen dioxide (NO2) to form nitric acid and / or nitrous acid in solution within the heap to continue the leaching step.

[0030] Recycling the nitric acid and / or nitrous acid produced within the heap in step (e) for use in the first irrigation solution reduces the loss of NO gas from the heap to 5%-30%.

[0031] The method may include capturing NO emitted from the surface of the stack. x gases and a step of recycling the evolved gases to the first irrigation solution in a gas scrubbing process to further reduce nitrate losses from the leaching process.

[0032] For subsequent capture, the NO emitted from the stack can be contained by covering the stack with a sealing cover (e.g., an insulated thermofilm or any impermeable covering). x The generated nitric oxide gas can be extracted from the stack using a suitable suction pump system. The NO x can be easily oxidized by the oxygen contained in the air fed from the bottom of the stack and contained in the exhaust NO x In gas.

[0033] Additional air or oxygen, or oxygen-enriched air, may be injected during the scrubbing process to ensure complete oxidation of NO to NO2. The generated NO2 may react with the scrubber solution to produce a scrubber effluent containing nitrous acid and nitric acid. In this way, the NO gas lost from the stack may be reduced to less than 5% and preferably 1% or less. The scrubber solution may be scrubbing water, raffinate solution, or any aqueous medium in which NO2 may be easily dissolved. Hydrogen peroxide or any other oxidant may also be added to the scrubber solution to help oxidize the unreacted NO absorbed into the solution from the gas phase.

[0034] The crushed ore subjected to acid agglomeration is agglomerated using acid alone without the addition of nitrates to increase the porosity of the ore.

[0035] The nitrate concentration in the first irrigation solution may be high and may range from 25 g / L to 80 g / L nitrate, preferably 30-50 g / L nitrate.

[0036] The nitrate concentration in the first irrigation solution can be controlled based on the mineral oxidation rate and the pile temperature so that it is in the range of 10 g / L to 80 g / L nitrate.

[0037] Air or oxygen, or oxygen-enriched air may be introduced into the pile at the base of the pile or at multiple points from the base of the pile to the top of the pile and / or at one or more levels above the base of the pile. The aeration rate may be controlled to be 0.01-0.05 Nm 3 / ht range to maximize the stack temperature (heat generation rate) and the NO from the stack x Gas losses are minimized.

[0038] The irrigation rate and aeration rate can be controlled to maximize heat generation within the pile, minimize NO loss, and maximize nitrate recirculation to the first irrigation solution. For example, but not limiting, the irrigation rate can be 2.5-6 L / hm 2 range, and the specific mass flow rate of air (Ga, in kg / hm 2 ) for irrigation rate (Gi, in kg / hm 2 ) can be in the range of 0.10-0.3.

[0039] After completion of the initial leaching step, the method may include a flushing step whereby the heap is flushed with low nitrate process water to recover excess nitrates in the heap.

[0040] Once the desired heap temperature has been reached by oxidation of the sulphide minerals (and in particular pyrite), and while taking the necessary steps to conserve the heat generated in the heap, the method may comprise the following additional steps:

[0041] f) flushing the pile with low nitrate raffinate or process water to remove excess nitrates;

[0042] g) irrigating the heap with a second irrigation solution comprising an acidic nitrate solution in a separate leaching step.

[0043] The nitrate concentration in the second irrigation solution may be low and range from 0.5 g / L to 15 g / L nitrate.

[0044] The sulfide mineral ore may be selected from chalcopyrite, pyrite, covellite, chalcocite, bornite, calcite, copper oxide minerals or nickel sulfide minerals. This is not restrictive.

[0045] The acid concentration in the first and second irrigation solutions may range from 5 g / L to 40 g / L and up to 50 g / L sulfuric acid.

[0046] The first irrigation solution contacting the ore in the heap leaching process reacts with dissolved iron in the ore to produce a solution oxidation potential of 700 to 1200 mV relative to SHE (standard hydrogen electrode).

[0047] The high oxidation potential results in exothermic oxidation of sulphide minerals contained in the ore, such as pyrite and chalcopyrite, generating heat and raising the pile temperature to a temperature in the range of 50°C to 85°C.

[0048] The method may be carried out at atmospheric pressure and ambient temperature in an environment external to the stack.

[0049] The crushing size distribution of the ore can be determined by the ore characteristics and can be within the range of 4 mm P 80 (80% through dimension) to 102mm P 80 range, including ROM samples. The particle distribution selected should contain a sufficient amount of fines to aid in the initial generation of heat by pyrite oxidation.

[0050] Nitrates and nitrites may be added in solution, or may be added to the ore as solid salts during the heap construction process.

[0051] The source of nitrate may be selected from nitric acid (HNO3), NaNO3, KNO3 or any other soluble inorganic nitrate.

[0052] The source of nitrite can be selected from nitrous acid (HNO2), NaNO2, KNO2 or any other soluble inorganic nitrite, or as a known impurity in nitrate.

[0053] In operations where acid agglomeration is an option, the amount of sulfuric acid added may be in the order of 5 kg / T to 20 kg / T, the amount of acid added being determined by:

[0054] • The acid requirement to leach the gangue minerals in the ore; for example carbonates, iron oxides and silicate minerals including chlorite and biotite.

[0055] • The amount of acid added required to form strong agglomerates and thereby improve the permeability of the heap consisting of accumulated agglomerated ore.

[0056] In the case where the nitrate is added as nitric acid, the sulfuric acid requirement will be based on the nitric acid (H + NO3 - ) of dissolved H + concentration.

[0057] The first and second irrigation solutions which come into contact with the ore during the leaching stage are acidic, having a pH below pH 3, and preferably below pH 2.

[0058] Each of the first and second irrigation solutions may contain iron, copper, and other dissolved cations and anions as leached product species.

[0059] During the leaching cycle, a recirculating process solution containing nitrates and nitrites can be used in ore irrigation.

[0060] The irrigation solution may be the raffinate solution from a solvent extraction operation, obtained from any part of a leaching unit (including gas scrubber effluent), or freshly prepared with acidified water by dissolving the desired ions and cationic species.

[0061] The rate of application of the irrigation solution and the rate of supply of air, or oxygen, or oxygen-enriched air are carefully adjusted to ensure that the NO released within the pile is x The gas is oxidized to nitrates and the NO x Gas or gas scrubbing, recirculating the generated nitrates in the irrigation solution. In this way, while capturing the NO discharged from the stack x In the case of gas, NO x The efficiency of oxidation of gases to nitrates within the stack ranges from 70% to 80%, or from 80% to 95% and up to 99%.

[0062] Description of the drawings

[0063] The invention is further described by means of embodiments with reference to the accompanying drawings, in which:

[0064] Figure 1a is a flow chart of one embodiment of a method according to the present invention, the method comprising first and second leaching steps;

[0065] Figure 1b is a flow chart showing another embodiment of the process of the present invention performed without a second leaching step;

[0066] Figure 2 A gas scrubber circuit according to the invention is shown;

[0067] Figure 3 is a temperature profile of a pile irrigated with a first irrigation solution and subsequently a second irrigation solution according to the method of the present invention;

[0068] Figure 4 is a temperature profile graph of a pile wherein irrigation is performed using the second irrigation solution followed by the first irrigation solution;

[0069] Figure 5 is a comparative graph of copper extraction, showing the effect of irrigation solutions;

[0070] Figure 6 is a graph comparing pyrite conversion over time with and without nitric acid regeneration.

[0071] Figure 7is a comparative graph of acid and nitrate concentrations over time with and without nitric acid regeneration;

[0072] Figure 8 is a comparative graph of solution potential over time with and without nitric acid regeneration;

[0073] Fig. 9 is a comparative graph of pyrite conversion over time with and without nitric acid regeneration;

[0074] Fig.10 is a comparative graph of acid and nitrate concentrations over time with and without nitric acid regeneration;

[0075] Fig.11 is a comparative graph of solution potential over time with and without nitric acid regeneration;

[0076] Fig.12 Column temperature profiles of Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention are shown;

[0077] Fig.13 shows pyrite dissolution curves of Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0078] Fig.14 shows copper dissolution curves of Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0079] Fig.15 shows chalcopyrite dissolution curves of Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0080] Fig.16 shows net acid consumption curves for Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0081] Fig.17 shows oxygen consumption curves of Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0082] Fig.18 shows nitrate consumption curves as sodium nitrate columns for Cases 1 to 3 and 5 to 7 according to an embodiment of the present invention;

[0083] Fig.19 The effect of acid in the irrigation solution or raffinate on copper recovery from ores with low acid consumption gangue and with high acid consumption gangue is shown;

[0084] Fig. 20 The effect of nitrate concentration on copper recovery is shown;

[0085] Fig.21The effect of aeration rate on copper recovery according to an embodiment of the present invention is shown;

[0086] Fig. 22 shows a comparison of copper extraction using different raffinate solutions according to an embodiment of the present invention;

[0087] Fig.23 shows a comparison of reagent consumption using different solutions according to an embodiment of the present invention; and

[0088] Fig.24 The column temperature profile affected by the nitrate concentration of the raffinate according to an embodiment of the present invention is shown.

[0089] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0090] FIG. 1a shows a simplified flow chart illustrating a method 10A of the present invention, which includes first and second leaching steps. FIG. 1b shows a simplified flow chart illustrating a method 10B of the present invention, which does not include a second leaching step. Method 10B is fully incorporated into method 10A; however, method 10A includes an additional leaching step. In the accompanying drawings, the same reference numerals are used to illustrate features common to each of methods 10A and 10B. Methods 10A and 10B can be used for leaching of primary copper sulfide ores, secondary copper sulfide ores, oxide copper ores, and mixed copper ores.

[0091] In each of the methods 10A and 10B (see FIGS. 1a and 1b , wherein the corresponding features of the method 10B are included in parentheses), ore is deposited 24A in the form of run of ore (ROM) ore 12 (12A) to form a pile 24. The ore 12 (12A) may be crushed in a crusher 14 (14A) to ensure that the crushed ore 16 (16A) has a suitable size as required. Preferably, the crushed ore has a P size of 4 mm. 80 (80% through the sieve) to 102mm P 80 .

[0092] In the leaching step 24B, a first irrigation solution 18 (18C) is applied on top of the heap 24. The first irrigation solution contains an acidic nitrate solution having a high nitrate concentration in the range of 25 g / L-80 g / L and a low nitrite concentration of 50-500 ppm, preferably 100-500 ppm.

[0093] The resulting high nitrate and nitrite drainage solution from the leaching step 24B is collected in the form of a pregnant leach solution 1 (PLS1) 26 (26A) in a PLS1 cell 28 (28A). PLS1 26 (26A) is rich in copper, nitrates and nitrites from the leached ore, as well as other cationic and anionic species. The PLS1 cell 28 (28A) feeds a solvent extraction (SX) unit 30 (30A) where copper is concentrated to produce an advance electrolyte solution 32 (32A) which is processed to recover metallic copper by electrowinning in an electrowinning cell chamber 34 (34A). The copper-removed PLS1 28 (28A) constitutes a high nitrate and nitrite raffinate solution 28B and is mixed with the saturated scrubber raffinate 36 (36A) to produce a high nitrate and nitrite raffinate 18A (18D), which is then collected in a high nitrate and nitrite raffinate tank 38. Nitrates 62 (62A) are added to the raffinate 18A (18D) if necessary, and the resulting solution 18B (18E) is discharged from the tank and recycled to the leaching step 24B as a high nitrate raffinate solution 18 (18C). Nitrates, acids and water may be added to either raffinate 1 or raffinate 2 to maintain the desired concentration.

[0094] During the leaching step 24B, the 3 Forced aeration 40 (40A) is applied to the bottom of the pile 24 and / or to one or more levels above the bottom of the pile at a rate of / hr.t.

[0095] As shown in Figure 1a, method 10A may include an optional second leaching step. In this regard, leaching step 24C is performed after leaching step 24B.

[0096] During the leaching step 24C, 0.01-0.05 Nm 3 Forced aeration 40 is applied to the bottom of the heap 24 and / or to one or more levels above the bottom of the heap at a rate of 100 t / hr.t.

[0097] During the leaching step 24C, a second irrigation solution in the form of a low nitrate raffinate solution 20 is applied to the heap 24 and collected in the drainage at the bottom of the heap 24 as a low nitrate enriched leach solution 2 (PLS2) 42 containing a high copper concentration and other cationic and anionic species from the leached ore.

[0098] PLS2 42 is collected in PLS2 cell 44 which feeds solvent extraction (SX) unit 30 where copper is concentrated to produce pre-electrolyte solution 32 which is processed to recover metallic copper by electrowinning in electrowinning cell chamber 34. The resulting copper-depleted and acid-enriched PLS2 42 constitutes low nitrate raffinate solution 20A which is collected in low nitrate and nitrite raffinate cell 46.

[0099] In the low nitrate and nitrite raffinate tank 46, fresh water 48 may be added as make-up water to compensate for water losses in the heap leaching circuit due to moisture in the leached residual ore, spills, leaks and evaporation. If necessary, sulfuric acid 50 may be added to replace the acid consumed by the ore in the leaching step 24C. The solution 20B from the tank 46 is recycled as low nitrate raffinate 20 to the leaching step 24C in the heap 24.

[0100] In the leaching steps 24B and 24C, nitrogen oxide gas (NO x )52(52A).

[0101] Nitric oxide (NO) released within the pile by the oxidation reaction of nitrates with sulfide minerals and the oxidation of Fe(II) to Fe(III) is oxidized by oxygen to form NO2, which is hydrolyzed by the solution within the pile to form nitrous acid and / or nitric acid, as shown by the simplified overall reaction:

[0102] Nitrous acid is formed; 2NO(aq)+1 / 2O2(aq)+H2O→2HNO2(aq); and

[0103] Nitric acid is formed; NO+3 / 4O2+1 / 2H2O=NO3 - +H + ).

[0104] refer to Figure 3 , NO x Gases may be exhausted from the stack, and therefore methods 10A and 10B include provisions to capture escaping acid mist and volatile oxide gases of nitrogen by scrubbing. In order to recover NO emitted from the surface of the stack 24, x The stack 24 is covered with a sealing cover of any impermeable material, such as a thermally insulating membrane 54 (54A) shown in dashed outline. A system of suction pumps 68 is used to transfer NO x (e.g., NO and NO2) 52 is drawn from the stack to a gas scrubber 56 (56A). It is expected that the NO contained in the stack xNitric oxide (NO) in the gas and in the gas discharged from the stack is readily oxidized by oxygen contained in the air added to the stack, or by additional air, or oxygen, or oxygen-enriched air injected during the gas scrubbing process to ensure complete oxidation of the nitric oxide gas (NO) to NO2, which is discharged from the stack and captured in the gas scrubber stage. The NO2 generated is expected to react with the raffinate, process water, or any aqueous medium 58 (58A) in which NO2 can be easily dissolved, and air or oxygen-enriched air 60 (60A) to form a scrubber raffinate solution 36 (36A), which will be richer in nitrates than the scrubber feed solution 58 (58A). Hydrogen peroxide (not shown) or any other oxidant may also be added to the scrubber solution to help oxidize the unreacted NO absorbed from the gas phase into the scrubber raffinate solution. In the scrubber 56 (56A), it is expected that the NO in the bulk gas stream will be oxidized to NO2 before it is discharged to the atmosphere. x The concentration was reduced from 50 ppm to less than 5 ppm.

[0105] The scrubber raffinate solution 36 (36A) is combined with the high nitrate raffinate 18A (18D) from the leaching step 24B to produce a solution 18B (18E), which is then recycled to the leaching step 24B as the high nitrate raffinate solution 18 (18C). In the high nitrate raffinate tank 38 (38A), nitrate 62 (62A) may be added as make-up nitrate to compensate for nitrate losses in the heap leach circuit. Sulfuric acid 64 (64A) may also be added to replace acid consumed by the ore in the leaching step 24B.

[0106] Referring to Figure 1 b, after the leaching step 24B, the heap is washed (24C) with water 66A and the resulting effluent 24X is transferred to the raffinate tank 38A.

[0107] 1 a , after the leaching step 24C, the heap is washed ( 24D) with water 66 and the resulting effluent 24X is transferred to a low nitrate raffinate tank 46 .

[0108] Leaching steps 24B and 24C ensure that the solution in contact with the ore 12 reaches a high oxidation potential of 750-1200 mV relative to the standard hydrogen electrode (SHE), resulting in rapid oxidation of copper sulfide minerals and iron sulfide minerals (including pyrite). The high solution oxidation potential achieved (750-1200 mV relative to SHE) increases the oxidation rate of sulfide minerals and pyrite, which results in an increase in the heap temperature, thereby increasing the rate of dissolution of metals from chalcopyrite and other related sulfide minerals.

[0109] No effective recycling of NO gas has been demonstrated in heap leaching processes operating at ambient pressure. Although NO2 and NO gas may be generated during the oxidation of minerals with nitrates and nitrites, the solubility of NO gas in aqueous solution is very low, while NO2 is easily hydrolyzed in water to form nitrous acid and nitric acid and is therefore easily reabsorbed into the leach solution (3NO2 + H2O = 2HNO3 + NO).

[0110] The consumption of sodium nitrate is the major contributor to the cost of heap leaching operations. The net consumption of nitrate depends on the ability to achieve in situ regeneration of nitrate within the heap according to the following reaction R1, which represents the overall reaction in which nitric oxide is oxidized by oxygen in the gas phase to nitrogen dioxide, which is subsequently hydrolyzed to nitric acid. The extent to which nitrate is regenerated in situ within the heap by reaction R1 depends on the residence time available within the mineral bed for gas phase reactions, which in turn depends on the aeration rate and the concentration of oxygen in the gas phase.

[0111] A portion of the nitric oxide generated by reactions R2 and R3 within the mineral bed of the pile does not react with oxygen and is lost from the mineral bed in the gas stream at the top of the pile or column, representing nitrate consumption.

[0112] NO(g)+3 / 4O2(g)+1 / 2H2O→H + +NO3 - Reaction R1

[0113] Fe(III) is produced by oxidation of Fe(II) according to reaction R2;

[0114] Fe(II)+4 / 3H + +1 / 3NO3 - →Fe(III)+1 / 3NO(g)+2 / 3H2O Reaction R2

[0115] S 0 +2NO3 - →SO4 2- +2NO(g) Reaction R3

[0116] FeS2+14Fe(III)+8H2O→15Fe(II)+2SO4 2- +16H + Reaction R4

[0117] CuFeS2+16Fe(III)+8H2O→Cu(II)+17Fe(II)+2SO4 2- +16H + Reaction R5

[0118] CuFeS2+4Fe(III)→Cu(II)+5Fe(II)+2S 0Reaction R6

[0119] The nitrate consumption for the leaching of pyrite and typical copper sulfide minerals from primary copper ores can be represented by the following equation, where γ is the fraction of nitric oxide gas lost from the mineral bed in the heap:

[0120] FeS2+5γNO3 - +15(1-γ) / 4O2+(1-5γ) / 2H2O→Fe 3+ +2SO4 2- +5γNO(g)+(1-5γ)H +

[0121] CuFeS2+17γ / 3NO3 - +17(1-γ) / 4O2+(1+17γ / 3)H + →Cu 2+ +Fe 3+ +2SO4 2- +17γ / 3NO(g)+(3+17γ) / 6H2O

[0122] Cu2S+10γ / 3NO3 - +5(1-γ) / 2O2+(2+10γ / 3)H + →2Cu 2+ +SO4 2- +10γ / 3NO(g)+(1+5γ / 3)H2O

[0123] CuS+8γ / 3NO3 - +2(1-γ)O2+8γ / 3H + →Cu 2+ +SO4 2- +8γ / 3NO(g)+4γ / 3H2O

[0124] The consumption of the key reactants nitrate, acid and oxygen depends on the amount of NO gas recycled as nitrate by reaction with oxygen in the pile, or by separate capture and oxidation of NO gas exhausted from the pile. Oxidation of NO gas to nitrate in the pile by aeration of the pile is the most effective recycling method. The effect of percentage fractional loss of NO gas on reagent consumption is shown in Table 1 below. For the exemplary results shown in Table 1, a 5% NO loss results in zero net acid consumption, while a NO loss below 5% results in net acid production (shown as negative acid consumption). Nitrate consumption increases proportionally with the increase in NO loss.

[0125] Table 1 Percentage of NO gas lost by heap leaching and resulting reagent consumption

[0126]

[0127] The results are based on the treatment of a primary copper ore containing 1% chalcopyrite, 0.24% chalcocite and 3% pyrite. Pyrite oxidation was 45% and total copper dissolution achieved was 82%.

[0128] Table 2 shows the results of the effect of aeration rate on the fraction of nitric oxide gas lost from the ore bed, γ, and the associated consumption of sodium nitrate. The results show that the aeration rate increases from 0.04 Nm 3 / ht reduced to 0.02Nm 3 / ht will reduce nitrate consumption expressed as sodium nitrate by 3-4kg / t processed ore.

[0129] Table 2 Effect of aeration rate on the fraction γ of nitric oxide gas lost from the ore bed and the associated consumption of sodium nitrate based on model predictions.

[0130]

[0131] The maximum nitrate consumption for economical recovery of metals from the ore is 10 kg / T of ore treated, and preferably 5 kg / T or less.

[0132] In the absence of nitrite ions, dissolution of pyrite by oxidation with nitrate ions is very slow. However, addition of small amounts of nitrite (as low as 50 ppm) can initiate oxidation of pyrite with a mixed potential increase of about 50-70 mV and a solution potential increase of above 0.9 V. Example

[0133] Example 1. Column leaching test

[0134] Applicants tested the performance of the process of the present invention (hereinafter referred to as the "Nitrothermal process") under the conditions shown in Table 3 below on a primary copper sample containing 80% chalcopyrite grading 0.49% copper as the main copper source and 3% pyrite.

[0135] Table 3: Column test conditions

[0136]

[0137] The samples were received as Run of Ore (ROM), blended to obtain representative samples and dry loaded in the three columns mentioned above. It is important to note that due to the use of a blasting system at the mine, the particle size distribution of the ROM is on average finer than standard ROM samples from other operations. 80 <2.5”.

[0138] Once loaded, the ore was irrigated with a raffinate solution, the composition of which is shown in Table 4 below. Columns 1 and 3 were initially irrigated with raffinate 1 until day 120 before switching to raffinate 2. On the other hand, column 2 was initially irrigated with raffinate 3 before switching to raffinate 1 on day 135. During the irrigation, 0.04 Nm 3 Aeration rate of / hr.t.

[0139] Table 4: Raffinate composition

[0140]

[0141] Figure 3 It is shown that the exothermic oxidation of pyrite causes the temperature in the column to increase as irrigation proceeds. A maximum value of 70°C is reached on day 80, which is maintained for 70 days before it begins to decrease. An average temperature of 50°C in the column is ideal for leaching of chalcopyrite, as can be observed in columns 1 and 3, respectively. However, as Figure 4 As shown, no temperature is generated in the column initially operated under bioleaching conditions (i.e., low nitrate conditions), and as Figure 5 As shown, copper extraction was minimal. However, once the decision was made to change the raffinate for this column at day 129, the temperature increase in the column took less than 10 days. The temperature increase was followed by a corresponding increase in copper extraction, with a maximum of 83% copper solubility obtained - see Figure 5 .

[0142] Example 2: Oxidation of pyrite by acidified nitrate solution

[0143] Experiments were conducted to study the oxidation of pyrite in a flask with sulfuric acid and sodium nitrate solutions over a range of acid and nitrate concentrations. Data measured included acid and iron concentrations, solution potential, and pyrite conversion as a function of reaction time. Pyrite conversion was calculated from iron concentration.

[0144] The overall reaction rate of ferrous iron in the chemical reaction can be written as:

[0145]

[0146] Where m FeS2 and V are the mass (mol) of pyrite and the volume (L) of the solution in the flask reactor, respectively.

[0147] Other species in the chemical reaction (i.e. FeS2, Fe 3+ , H + 、NO3 - and NO), can be expressed similarly to the above equation.

[0148] Experiment 1: Nito60

[0149] The initial conditions for the Nitro 60 test were: [Fe2+]0=0.073 g / L, [Fe3+]0=1.24 g / L, [H2SO4]0=141 g / L, [NO3-]0=88 g / L and [FeS2]0=125 g / L (50 g of pyrite in 0.4 L of leach solution). The solid (pyrite) loading for the flask test is typical for heap leaching with a pyrite grade of approximately 1 wt%.

[0150] Figure 6 Measured and calculated pyrite conversions during a 22 day leaching test are shown. The dashed line is the calculated conversion without nitric acid regeneration, while the solid line is the calculated conversion with nitric acid.

[0151] Figure 7 The measured and calculated acid concentrations and the calculated nitrate concentrations during the leaching test are shown. The solid and dashed lines are the calculated concentrations with and without nitric acid regeneration, respectively.

[0152] Figure 8 Shown are the measured and calculated solution potentials during the leaching test. The solid and dashed lines are calculated with and without nitric acid regeneration, respectively.

[0153] Figure 7 The calculation results in show that the initial nitrate in the leaching solution is consumed after about 10 days without nitric acid regeneration. At the same time, the calculated acid concentration ( Figure 7 )、solution potential( Figure 8 ) and pyrite conversion rate ( Figure 6 The effect of including nitric acid regeneration in the reaction scheme is shown by the solid line, which is clearly much more consistent with the measured data.

[0154] The fraction of nitric oxide (γ) that is not oxidized to nitric acid is γ = 0.39 according to the following equation:

[0155] The overall oxidation stoichiometry of pyrite can be written in terms of γ as:

[0156]

[0157] For γ = 0.39, it can be seen that dissolving 1 mol of FeS2 consumes 0.95 mol of H + and 1.95 mol NO3 - , which is consistent with Figure 7 The final concentrations of acid and nitrate were the same.

[0158] In the absence of nitric acid regeneration, γ = 1, and dissolving 1 mol of FeS2 consumes 4 mol of H +and 5 mol NO3 - .

[0159] The results show that in the oxidation of pyrite by acidic nitrate as shown in the reaction in paragraph

[00106] , regenerating nitric acid under defined conditions significantly reduces nitrate consumption, increases the extent of pyrite oxidation, and maintains a higher solution oxidation potential (Eh, mV, relative to SHE).

[0160] Experiment: Nitro 30

[0161] The initial conditions for the Nitro 30 test were: [Fe2+]0=0.067 g / L, [Fe3+]0=1.28 g / L, [H2SO4]0=163 g / L, [NO3-]0=44 g / L and [FeS2]0=125 g / L (50 g of pyrite in 0.4 L of leaching solution).

[0162] Figures 9 to 11 The measured and calculated pyrite conversion, acid and nitrate concentrations, and solution potential during the 22-day leaching test are shown. The solid and dashed lines are the calculated results with and without nitric acid regeneration, respectively. The trend is consistent with that of Nitro 60.

[0163] The fraction of nitrogen monoxide that is not oxidized to nitric acid according to reaction equation 1 (R1) is γ = 0.13. That is, 13% of the escaped NO gas is lost, or 87% of the NO gas is recycled to regenerate nitrates and acids.

[0164] For γ = 0.13, it can be seen that dissolving 1 mol of FeS2 generates 0.35 mol of H + And consume 0.65 mol of NO3 - ,and Fig.10 The final concentrations of acid and nitrate were the same.

[0165] The results showed that the regeneration of nitrate was greater in test Nitro 30, which lost only 13% of NO gas, indicating improved pyrite oxidation, reduced acid consumption and higher solution oxidation potential.

[0166] Example 3: Demonstration of the effect of operating conditions on leaching performance

[0167] Extensive experimental testing was conducted in a 10 m simulated column (the simulated column design is given in U.S. Pat. No. 7,727,510 B2, June 1, 2010). The results of the experimental program were used to test the effects of process variables and reagent additions in Nitrothermal leaching, which defines conditions for achieving high heat generation rates by pyrite oxidation and maximizing copper recovery at minimal nitrate consumption. Trials were conducted with crushed primary (deep rock) copper ore and run-of-mine primary (deep rock) copper ore.

[0168] The model parameters were derived from the test data and the model outputs were tested and validated against the results of a 10 m simulated column test. The model results were then used to describe the observed results. Examples of column experiments completed as 10 separate case studies are summarized in Table 6 below and the results of the case studies showing the effects of operating conditions and reagent concentrations are shown in Figures 12 to 21 middle.

[0169] The ore characteristics used in the simulated column leaching tests are listed in Table 5 below:

[0170] Table 5: Ore characteristics

[0171] project unit value Particle size <![CDATA[P 80 (mm)]]> 50 Pyrite content quality% 3 Total Cu quality% 0.43 Fraction of Cu as chalcopyrite ％ 81 Low GAC* Biotite + Chlorite quality% 1 High GAC*biotite+chlorite quality% 10

[0172] *GAC – Gastrointestinal Acid Consumption

[0173] Test Conditions Case Studies 1 to 10

[0174] Table 6 Column Case Study

[0175]

[0176] Acid and nitrate concentrations refer to the concentrations in the irrigation solution of the 10 m simulated column test.

[0177] Gangue refers to acid-consuming non-sulfide minerals in an ore, and is primarily silicate minerals such as chlorite and biotite. "Low" refers to low GAC (gangue acid consumption) (chlorite and biotite are relatively low in content), while "high" refers to high GAC (usually chlorite and biotite are relatively high in content).

[0178] Air is the aeration rate of the column expressed in Nm per hour per metric tonne of ore loaded into the column. 3 (Here Nm 3 Defined as air flow at 0°C and 101.325 kPa).

[0179] Explanation of the test conditions checked:

[0180] Case studies 1 to 3 show that at 50 g / L nitrate concentration and 0.04 Nm3 The effect of increasing the acid concentration of low-acid-consuming gangue at a fixed aeration rate of 1.5 ht / ht.

[0181] Case 4 and Case 8 show the effect of reduced nitrate concentration in the irrigation solution on low- and high-acid-consuming gangue, respectively.

[0182] Case studies 5 to 7 show the effect of acid concentration on high acid consumption gangue.

[0183] Case studies 9 and 10 show the impact of lower aeration rates.

[0184] Summary of findings from case studies 1-10:

[0185] a) Higher pyrite oxidation rates lead to higher temperatures.

[0186] b) Higher temperatures increase chalcopyrite dissolution and therefore copper recovery.

[0187] c) For the ore type considered, a higher acid concentration of 30 g / L is necessary to maintain nitrate oxidation of the sulfide minerals and achieve maximum copper recovery.

[0188] d) NAC increases with increasing acid concentration in the irrigation solution.

[0189] e) Ores with relatively high gangue acid consumption required increased acid addition, for example 40 g / L in the irrigation solution for Case 7, in order to sustain sulfide mineral oxidation reactions and maintain copper recoveries close to 80%.

[0190] f) Nitrate addition of 50 g / L in the irrigation solution ensured maximum copper recovery.

[0191] g) 0.04Nm 3 The higher aeration rate of 1.5 ht / ht ensured maximum copper recovery and resulted in relatively low nitrate consumption (as shown by the results of Cases 3 and 7).

[0192] Example 4: Gas capture and scrubbing tests

[0193] A sample of native sulphide loaded into a 10 m column was leached under nitrate conditions with forced aeration introduced at the bottom of the column. The column off-gases were sent by a suction system to a scrubber containing 400 L of water and after 4 days of operation the water was analysed for nitrates and acids. The results obtained showed that after the 4th day, when the water test was stopped, the pH had dropped from pH 6.8 to pH 1.5 and the solution contained 19.3 g / L of acid and 26 g / L of nitrate content - see Table 7 below. This solution is suitable as a process liquid for recycling in the leaching process. For a column loaded with 10 t of fresh ore, the nitrate contained in the scrubber solution was equivalent to 1 kg nitrate / t ore recycled to the process during 4 days of gas capture. The recovery of the escaping gases means a substantial reduction in the process operating costs. The recovered nitrates reduce the process nitrate consumption from 15 kg / t (zero NO captured) to 26 g / t (zero NO captured). x ) is reduced to only 3kg / t (NO is recovered by gas scrubber operation) x gas).

[0194] Table 7: Scrubber Solution Analysis Results

[0195] pH Acid(g / L) Nitrate (g / L) Water before testing 6.8 0 0 Water after testing 1,5 19,3 26

[0196] The column off-gas was also measured before and after the gas scrubber unit. The results show that the gas scrubbing efficiency using water is greater than 90%, Table 8. The gas before the scrubber contains more NO, as it is expected that most of the NO2 produced reacts with the raffinate solution directly in the column.

[0197] Table 8: Column gas results

[0198] NO(ppm) <![CDATA[NO2(ppm)]]> Before scrubber 40 20 After scrubber 5 3

[0199] The process of the present invention provides an efficient solution for nitrate regeneration, reducing the operating costs of the process. Furthermore, the process ensures a high oxidation potential to allow efficient leaching of sulfide mineral ores without the need for agglomeration and maturation steps.

[0200] Example 5 - Two-stage leaching

[0201] The effect of changing the raffinate solution from high nitrate to low nitrate on the total nitrate demand of the process was demonstrated using samples having the properties shown in Table 9 below:

[0202] unit M2 M1 <![CDATA[Ore PSD, P 80 > inch 1.5 0.875 Chalcopyrite ％ 75 75 irrigation: High Nitrate (50g / L) yes yes Low nitrate (30 and 10 g / L) yes no

[0203] Sample M1 was irrigated with a high nitrate raffinate solution containing only 50 g / L nitrate throughout the leaching cycle, while in sample M2, the raffinate was changed from high nitrate to low nitrate once the desired leaching temperature was reached. After 200 days of irrigation, the results showed no significant difference in the final extraction (83% vs 81%) of the columns operated with or without changing the raffinate solution - Fig. 22 . This is primarily because the change in raffinate is only made once the column has reached the temperature required for leaching chalcopyrite (>55°C), and thereafter it is only necessary to maintain that temperature and ensure that sufficient oxidant (high iron / nitrate) is available for continued mineral leaching. The benefit of changing to a lower nitrate concentration is a saving in reagent consumption (sodium nitrate). The results show that 28 kg / t of NaNO3 was consumed in column leaching trial M1, in which only 50 g / L of high nitrate raffinate was used. In column trial M2, which used a two-stage leaching, this consumption was reduced to 15 kg / t NaNO3, in which the first stage irrigation used a high nitrate concentration, and the second stage irrigation used a low nitrate concentration (30 g / L and 10 g / L), see Fig.23 Thus, the two-stage leaching achieved a 46% saving in sodium nitrate reagent. x The capture of the gas is limited to 80%, which is why the sodium nitrate consumption is 15 kg / t.

[0204] In another test, using a sample with similar characteristics to M2, the effect of varying the raffinate solution on the heat generated was shown. The column was initially irrigated with a 50 g / L nitrate raffinate solution and once the desired temperature was reached the nitrate raffinate concentration was reduced to 30 g / L and subsequently to 10 g / L. The results showed that despite the reduction in the nitrate concentration of the raffinate irrigation solution, the temperature remained high and suitable for chalcopyrite leaching - see Fig.24 .

Claims

1. A method for extracting copper from a sulfide mineral ore selected from ROM ore, crushed ore or crushed ore subjected to acid agglomeration, the method comprising the following steps: a) piling up ore to form a heap; b) In the leaching step, a nitrate-containing solution (NO3 - ) solution and 50ppm to 500ppm nitrite (NO2 - ) to irrigate the heap, thereby causing oxidation of sulfide minerals within the heap; c) adding air or oxygen, or oxygen-enriched air to the stack; d) oxidizing nitric oxide gas released during oxidation of sulfide minerals in the heap with oxygen to form nitrogen dioxide (NO2); and e) hydrolyzing the nitrogen dioxide (NO2) to form nitric acid and / or nitrous acid in a first irrigation solution within the heap to continue the leaching step and reduce the loss of nitric oxide from the heap.

2. The method of claim 1, wherein the loss of nitric oxide gas from the stack is reduced to 5% to 30%.

3. The method of claim 1 including the step of capturing nitric oxide gas exhausted from the surface of the pile and recycling the escaping gas to the first irrigation solution in a gas scrubbing process.

4. The method of claim 3, wherein the nitric oxide gas is contained for subsequent capture by covering the stack with an impermeable cover.

5. The method of claim 4, wherein the nitric oxide gas is pumped from the stack by a suction pump system.

6. A method according to claim 3 or 4, wherein the nitric oxide gas leaving the stack is oxidised by oxygen contained in air added to the stack to form nitrogen dioxide (NO2).

7. A method according to claim 6, wherein additional air or oxygen, or oxygen-enriched air is injected during the scrubbing process to ensure complete oxidation of the nitric oxide gas, thereby generating nitrogen dioxide (NO2).

8. The method of claim 7, wherein the generated nitrogen dioxide reacts with a scrubber solution to produce a scrubber effluent.

9. A method according to claim 8 including the step of adding an oxidant to the scrubber solution to oxidise any unreacted nitric oxide gas.

10. The method according to claim 1, wherein the crushed ore subjected to ore agglomeration is agglomerated with acid only without adding nitrate to increase the porosity of the ore.

11. The method according to any one of claims 1 to 10, wherein the nitrate concentration is in the range of 25 g / L to 80 g / L.

12. The method according to any one of claims 1 to 10, wherein the nitrate concentration is in the range of 30 g / L to 50 g / L.

13. A method according to any one of claims 1 to 12, wherein air or oxygen, or oxygen-enriched air, is introduced into the stack at the base of the stack or at a plurality of points from the base of the stack to the top of the stack.

14. The method according to any one of claims 1 to 13, wherein the aeration rate is controlled so that it is within 0.01 Nm 3 / ht to 0.005Nm 3 / ht range.

15. The method according to any one of claims 1 to 14, wherein the irrigation rate is 2.5 L / hm 2 Up to 6L / hm 2 range.

16. The method according to claim 15, wherein the specific mass flow rate (Ga, in kg / hm2) of air 2 ) for irrigation rate (Gi, in kg / hm 2 ) is in the range of 0.10 to 0.

3.

17. The method according to claim 1, comprising the following additional steps: f) flushing the stack with raffinate or process water to remove excess nitrates; and g) irrigating the heap with a second irrigation solution comprising an acidic nitrate solution in a separate leaching step.

18. The method of claim 17, wherein the nitrate concentration in the second irrigation solution is low and ranges from 0.5 g / L to 15 g / L nitrate.

19. The method of any one of claims 1 to 18, wherein the acid concentration in the first irrigation solution and the second irrigation solution is in the range of 5 g / L to 40 g / L.

20. The method of any one of claims 1 to 19, wherein the first irrigation solution in contact with the ore reacts with dissolved iron in the ore to produce a solution oxidation potential of 700 mV to 1200 mV SHE (standard hydrogen electrode).

21. The method of claim 20, wherein the stack temperature is increased such that it is in the range of 50°C to 85°C.

22. A method according to any one of claims 1 to 21 carried out at atmospheric pressure and ambient temperature in an environment external to the stack.

23. The method according to any one of claims 1 to 22, wherein the source of nitrate is selected from nitric acid (HNO3), NaNO3, KNO3 or any other soluble inorganic nitrate.

24. A method according to any one of claims 1 to 23, wherein the source of nitrite is selected from nitrous acid (HNO2), NaNO2, KNO2 or any other soluble inorganic nitrite.

25. The method of any one of claims 1 to 16, wherein the first irrigation solution is acidic having a pH below pH 3.

26. The method of any one of claims 17 to 25, wherein the second irrigation solution is an acid having a pH below pH 3.

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